Known apparatus for enabling detection of core differential pressure and injection of a neutron absorbent into a core of a nuclear reactor generally includes two separate tubes, or conduits, constructed of stainless steel having a high carbon content. In one particular embodiment, one tube has a smaller diameter than the other tube, and the smaller diameter tube is positioned within the larger diameter tube to form a tube assembly. The tube assembly extends in the reactor pressure vessel (RPV), from an opening formed in the RPV wall to a socket. A first tube extends from the socket to an elevation within the pressure vessel above the core plate, and the open end of the first tube within the pressure vessel is exposed to pressures at the elevation above the core plate. The first tube is in flow communication with the larger diameter tube.
A second tube extends from the socket and to an elevation below the core plate. The open end of the second tube within the pressure vessel is exposed to pressures at the elevation below the core plate. The second tube is in flow communication with the smaller diameter tube.
In the one embodiment, at the exterior of the vessel wall at the location of the opening, a nozzle extends from the wall. The nozzle has a bore with a diameter greater than the outer diameter of the smaller diameter tube. The opening in the vessel wall has a diameter about substantially equal to the diameter of the bore. The smaller diameter tube extends through the opening in the wall and into the nozzle bore. A first port of the nozzle is in flow communication with the channel of the smaller diameter tube and a second port of the nozzle is in flow communication with the larger diameter tube. Pressure meters may be attached to the first and second ports of the nozzle.
In operation, the pressures within the pressure vessel at the elevations of the open ends of the tubes are communicated through the tubes to the pressure meters coupled to the nozzle ports. Utilizing the pressure readings from the respective pressure meters, a core differential pressure may be determined. Core differential pressure, as is well known, may be utilized to control reactor operations.
In addition, in the event that a liquid neutron absorbent must be injected into the reactor pressure vessel, the absorbent may be injected into the smaller diameter tube at the first nozzle port. The liquid neutron absorbent will flow through the smaller diameter tube and into the pressure vessel from the open end of such tube. As a result, the neutron absorbent will be injected into the reactor pressure vessel at an elevation below the core plate, which generally is a desirable location for injection of such an absorbent.
With respect to known differential pressure and standby liquid control line apparatus, creviced weld connections typically are used to weld the stainless steel tubes to support brackets. In addition, sockets and other connectors may be used in order to position the tubes in the desired locations and elevations within the core, and the tubes typically are welded to such sockets and connectors. The use of such welds, in combination with the high carbon content stainless steel tube material and exposure to the reactor environment, may result in intergranular stress corrosion cracking (IGSCC) of the tubes.
Of course, such IGSCC could lead to a failure of one or both of the tubes. Failure of the inner, smaller diameter, tube of the tube assembly may result in the loss of the ability to determine the core differential pressure. Failure of the outer, larger diameter, tube of the tube assembly could possibly result in an inaccurate core differential pressure reading, particularly if the discharge water flow from a jet pump impinges on the failed region of the outer robe. An inaccurate core differential pressure reading, or total loss of the ability to obtain such reading, may adversely affect reactor operation, including even possibly requiring shutting down the reactor to perform repairs.
It would therefore be desirable to provide a core differential pressure and neutron absorbent injection apparatus which reduces the possibility for IGSCC, thereby reducing the possibility for failure of the apparatus. In addition, it would be desirable to provide such an apparatus which can be utilized to replace existing core differential pressure and neutron absorbent injection apparatus presently installed in nuclear reactors in the event that a failure is ever detected or suspected.